(1) Field of the Invention
This invention relates to a power semiconductor device and a fabrication method thereof, and more particularly relates to a power semiconductor device with trench bottom heavily-doped polysilicon structures and a fabrication method thereof.
(2) Description of the Prior Art
In contrast with traditional planar power semiconductor device which features horizontal conductive current flowing along the surface layer of the base, the trenched power semiconductor device has the gate electrode embedded in a gate trench to change the direction of gate channel so as to generate a vertical conductive current flow. Therefore, size of the unit cell of the power semiconductor devices can be reduced to enhance cell integration. The power semiconductor devices commonly used in power industry include metal oxide semiconductor field effect transistor (MOSFET), insulated gate bipolar transistor (IGBT), and etc.
Energy loss of power semiconductor devices can be sorted as conducting loss due to conductive resistance and switching loss resulted from gate charge. It is well known that switching loss can be improved by reducing input capacitance (Ciss) and reverse transfer capacitance (Crss) of the power semiconductor device. However, in order to reduce input capacitance (Ciss) and reverse transfer capacitance (Crss), the fabrication process usually becomes quite complicated and the fabrication cost is thus increased.
Accordingly, it is an important issue in the art to figure out a simpler method, which may reduce input capacitance (Ciss) and reverse transfer capacitance (Crss) of the power semiconductor devices and can be applied to the present power semiconductor fabrication process easily.